| 摘要 |
A method for focusing by using a pre-flash is provided. The method includes the following steps. First, the image sensor captures a first image of the object, wherein the average brightness of the first image is calculated to be Y<SUB>0</SUB>. Next, the image sensor captures a second image of the object with the aid of a first pre-flash having a first energy, wherein the average brightness of the second image is calculated to be Y<SUB>1</SUB>. Afterwards, the image sensor captures a third image of the object with the aid of a second pre-flash having a second energy, wherein the average brightness of the third image is calculated to be Y<SUB>2</SUB>. Then, the distance D to the object is calculated according to the brightness Y<SUB>0 </SUB>and the difference DeltaY between Y<SUB>1 </SUB>and Y<SUB>2</SUB>. Finally, the image sensor adjusts the focus according to the distance D.
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